The total demand for methyl methacrylate (MMA) in the world wide market is now over 2 million tons and Asia, USA and Europe lead the market. In Asia, the demand for MMA in 2000 was approximately 750,000 tons, which was 4-5% increased from the previous year (400,000 tons in Japan; 110,000 tons in Taiwan; 90,000 tons in Korea; 80,000 tons in China and 70,000 tons in others). MMA demand in Asia is expected to increase further by an average of 4-5% per year owing to the growing demand in each country including China, Japan and others.
In Asia, MMA monomer has been mostly used for copolymer resins such as acrylonitrile-styrene (AS) and acrylonitrile-butadiene-styrene (ABS), paints for buildings and cars, paper coating, plastic, and resin modifier such as methylmethacrylate-butadiene-styrene (MBS).
In spite of the increasing demand for MMA, the production of acrylonitrile byproduct has been always short and thereby new production methods have been tried. One example is the gas phase oxidation based production established by Nippon Shokubai in 1982, which was the first in the world that uses isobutylene as a raw material. Since then, Mitsubishi Rayon, Sumitomo Chemical, and Kuraray/Mitsui Chemicals have initiated industrialization of MMA monomer by taking advantage of the gas phase oxidation. Another example is MAN process developed by Asahi Kasei by using methacrylonitrile (MAN). Mitsubishi Gas Chemical succeeded in industrialization of MMA by using novel acetone cyanohydrin (ACH) method which does not generate waste acid. KMC and FPC in Taiwan produce MMA by ACH method, while LG MMA and Honam Petrochemical Corp. in Korea, That MMA in Thailand and Singapore MMA Monomer in Singapore produce MMA by gas phase oxidation method.
Studies on the catalyst containing heteropoly acid as an active ingredient which is used for the partial oxidation of methacrolein into methacrylic acid by gas phase oxidation have been continued since the first commercialization in 1980s.
To produce heteropoly acid, MoO3 and V2O5 precursors are reacted with H3PO4 in the presence of water solvent at the temperature of at least 80° C. or ammonium paramolybdate and ammonium paravanadate are dissolved together in water. Details of the methods are described in the publication made by Tsigdinos, et al (Inorganic Chemistry, 7(3), p 437 (1968)).
U.S. Pat. No. 4,558,028 (granted on Dec. 10, 1985) describes a catalyst represented by MoaPbAcBdCeDfOx (A is one or more elements selected from the group consisting of As, Sb, Ge, Bi, Zr and Se; B is one or more elements selected from the group consisting of Cu, Fe, Cr, Ni, Mn, Co, Sn, Ag, Zn and Rh; C is one or more elements selected from the group consisting of V, W, and Nb; D is one or more elements selected from the group consisting of alkali metals, alkali earth metals and Ti; a is 12; b is 0.5-4; c is 0-5; d is 0-3; e is 0-4; f is 0.01-4 and x is the value indicating the oxidation of each element). The catalyst that is defined as the above needs to be dried, molded and fired in the presence of oxygen or nitrogen at 300-500° C. to be a final catalyst product. In general, the catalyst is molded as a pellet of 5 mm in diameter and 5 mm in length and at this time, decomposable ammonium or nitrate salt is decomposed to be a catalyst having the right structure and composition.
U.S. Pat. No. 4,621,155 (granted on Nov. 4, 1986) describes a method of preparing a heteropoly acid catalyst in which nitrogen containing pyridine, piperidine or peperazine is additionally included to increase plasticity, physical strength and reproducibility of catalyst production.
This method of preparing a heteropoly acid catalyst depends on the precursor of a metal component, but generally nitrate (NO3−) is used.
U.S. Pat. No. 6,333,293B1 (granted on Dec. 25, 2001) describes a method of preparing a catalyst. In this method, ammonium paramolybdate and ammonium paravanadate are dissolved in heated water, followed by stirring. Then, proper amount of 85% H3PO4 is added thereto and cesium nitrate and copper nitrate are additionally added. The mixed solution is heated and dried to give a catalyst.
U.S. Pat. No. 6,458,741B2 (granted on Oct. 1, 2002) describes a method of preparing a catalyst. In this method, ammonium paramolybdate, ammonium metavanadate and pyridine are added to 85% H3PO4, to which nitric acid, cesium nitrate and copper nitrate are additionally added, followed by co-precipitation. Then the precipitate is heated and dried to give a catalyst. According to this patent, the ratios of NH4/Mo12 and NH4/NO3 included in the precursor affect the activity and selectivity of the catalyst.
In spite of the development of various methods for producing a heteropoly acid catalyst, the low activity of the conventional heteropoly acid catalyst is still a problem. Therefore, it is required to improve the methacrolein conversion rate and selectivity in gas phase oxidation and the low productivity resulted from low yield as well.